Field of the Invention
The present invention relates to a reaction chamber for processing a substrate wafer. The chamber is formed of a wafer holder for receiving the substrate wafer, a convection plate, which is disposed above the wafer holder, for suppressing convective movements over the substrate wafer, and a gas distributor plate which is disposed on a side face of the reaction chamber, for distributing process or purge gases which flow in.
In the field of semiconductor fabrication, an increasingly large number of thermally activated processes, such as for example annealing, thermal oxidation or chemical vapor deposition (CVD), are being carried out in single-wafer installations. One reason for this is that the reduced throughput compared to batch operation can be compensated or even overcompensated for at a higher temperature as a result of a shorter process time. This trend is being reinforced considerably by the transition to larger wafer diameters, for example from 200 mm to 300 mm. A further reason is that in single-wafer processes there are often exclusive process conditions that can no longer be achieved by stacked processing.
A fundamental problem of such processes is that of achieving a uniform temperature over the substrate wafer which is to be processed, in particular when using wafers with large diameters of 200-300 mm, as are becoming increasingly widespread in semiconductor fabrication. This problem has been linked to convective movements that are caused by different temperatures on the substrate wafer and at the walls of the reaction chamber. To suppress the convective movements, it is proposed, in Published, Non-Prosecuted German Patent Application DE 197 47 164 A, for a convection plate to be disposed above the substrate wafer, which plate, in the case of a rotatable wafer holder, can rotate together with the holder. To be able to effectively suppress the convective movements, the distance between the convection plate and the wafer holder must not be selected to be excessively great. The distance is preferably between 5 and 10 mm. Within this range, convective movements are effectively eliminated without there being any interaction between the substrate wafer and the convection plate.
To achieve better process uniformity, the substrate wafer that is to be processed is mounted on a disk-like support plate that is rotated at a rotational speed of typically 10-100 rpm (revolutions per minute). The substrate wafer together with the carrier plate is generally rotating throughout the entire duration of the process cycle. The rotation is only stopped for loading and unloading of the substrate wafer.
In order for process and purge gases to be supplied, reaction chambers of this type often have a gas inlet in the form of a gas distributor plate that distributes the gas as uniformly as possible over an entire side face of the chamber. This is usually achieved by a configuration of openings that are distributed uniformly over the gas distributor plate. After a processing step has ended, the process gas is extracted via a gas outlet disposed on the opposite side of the reaction chamber, and, if necessary, the chamber is purged using a purge gas.
By way of example, in the case of a single-wafer rapid thermal processing (RTP) reactor, which is used, inter alia, for rapid thermal oxidation (RTO), the reaction chamber is purged with nitrogen after the oxidation operation. It is an essential condition for a high yield during the following steps of the process cycle that the oxygen be removed as completely as possible. Since the throughout of an installation of this type is partially determined, to a considerable extent, by the purge time, it is essential to minimize the purge time until an acceptable oxygen concentration is reached.
In the reaction chamber described above, after the introduction of the convection plate in order to achieve a greater temperature uniformity over the substrate wafer, the problem has arisen that the purge time has had to be made much longer in order for the oxygen to be removed from the chamber. Since increasing the purge flow rate to approximately 100 slm (Standard Liters per Minute) did not lead to sufficient removal of the oxygen, it was necessary to increase the purge time from what was previously a few seconds to one minute. However, such a long purge time already represents a considerable proportion of the overall process time and is therefore not economically acceptable.
It is accordingly an object of the invention to provide a reaction chamber for processing a substrate wafer and a method for operating the chamber which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, in which, following a treatment step, a thorough purge step can be carried out quickly. Furthermore, it is intended to provide a method for operating a reaction chamber of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a reaction chamber for processing a substrate wafer. The reaction chamber contains a wafer holder for receiving the substrate wafer to be processed, and a convection plate disposed above the wafer holder. The convection plate suppresses convective movements over the substrate wafer. A gas distributor plate is disposed on a side face of the reaction chamber. The gas distributor distributes process and purge gases which flow in. A flow plate is disposed on the gas distributor plate and extends substantially in a plane perpendicular to the gas distributor plate.
According to the invention, a reaction chamber of the generic type has the flow plate disposed on the gas distributor plate and extends substantially in a plane that is perpendicular to the gas distributor plate.
It has been discovered by the present inventor that the insufficient gas purging in reaction chambers of the generic type relates primarily to the area between the substrate wafer and the convection plate and results from a rolling circulatory movement upstream of the gas distributor plate. With the geometry of the conventional reaction chamber, the gas flow then tends, on account of the lower flow resistance at the sides of the wafer holder/substrate wafer/convection plate stack, to run from the gas inlet to the gas inlet. The result is a recirculating movement between the plates, which leads to closed flow lines and therefore to areas in which gases are trapped for a relatively long time.
Furthermore, it has emerged that the effect is further intensified by the rotary movement of the plates, which generally also takes place during the purging operation. In addition, the distance between the wafer holder and the convection plate has to be kept relatively short, in order to be able to suppress the convective movements over the substrate wafer. The result is a relatively high flow resistance for the flow between the substrate wafer and the convection plate, which makes the above-mentioned problems even worse.
The above-mentioned circulating movement is suppressed by the flow plate that is now additionally provided, and the gas flow is increasingly guided into the area between the substrate wafer and the convection plate. The changed flow conditions in the reaction chamber lead to the purge gas passing more successfully into the particularly critical area between the substrate wafer and the convection plate, making the required purge time considerably shorter.
The flow plate is preferably disposed approximately at the level of the convection plate on the gas distributor plate, so that the flow plate extends from the gas distributor plate to the convection plate and leaves only a relatively small intervening space for gas flowing through. As a result, the gas flow is guided particularly effectively into the space between the substrate wafer and the convection plate. Furthermore, the flow plate can extend right up to the convection plate.
In a preferred embodiment, the intervening space between the flow plate and the convection plate is large enough for sufficient purge gas to pass through the intervening space into the area above the convection plate, in order for a sufficient purging action to be achieved there as well.
In a further preferred embodiment, the profile of the chamber-internal edge of the flow plate is matched to the shape of the convection plate, in such a manner that a uniform distance between the convection plate and the flow plate is achieved over a wide area. For example, if the convection plate is circular, the flow plate may be in the shape of a rectangle with a cutout that is in the shape of a segment of a circle. As a result of this measure, it is obvious that a particularly large portion of the gas flow is guided into the area between the substrate wafer and the convection plate, although as the distance between the flow plate and the convection plate decreases, the flow of purge gas into the area above the convection plate also decreases. Therefore, the shape and size of the flow plate are expediently adapted to the geometry of the reaction chamber in such a way that sufficient purge gas passes into the area between the substrate wafer and the convection plate and into the area above the convection plate.
The gas distributor plate expediently has a plurality of gas outlet openings that are distributed over the plate surfaces. In a preferred embodiment, the gas outlet openings are disposed exclusively in the area below the flow plate, so that process and purge gases flow into the reaction chamber only below the flow plate. This may be advantageous in particular if the distance between the flow plate and the convection plate is so great that sufficient purge gas passes into the space above the convection plate from below. However, if this intervening space is small, it is generally more advantageous for gas outlet openings also to be provided in the gas distributor plate above the flow plate.
Since the substrate wafer is generally heated with a lamp array from the top side and/or the underside, it is advantageous for the gas distributor plate and/or the flow plate to be formed from quartz glass. Furthermore, it may be expedient for the gas distributor plate and the flow plate to be produced integrally.
In operation, the substrate wafer is processed in the reaction chamber as a result of the substrate wafer being introduced into the chamber, a process gas, such as, for example, oxygen, being fed to the chamber, a processing step, for example a RTO, being carried out on the substrate wafer, and then the chamber being purged as a result of a purge gas, such as, for example, nitrogen, being fed via the gas distributor plate.
To increase process uniformity, it is preferable for the wafer holder is rotated while the processing step is being carried out. For the step of purging the chamber, it has proven advantageous if the rotation of the substrate wafer is switched off while the chamber is being purged.
Although the following text relates predominantly to the use of the reaction chamber in conjunction with semiconductor fabrication, the described reaction chamber for processing the substrate wafer and the method for its operation can also be used for the deposition of thin films on substrates made from glass or plastic.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a reaction chamber for processing a substrate wafer, and a method for operating the chamber, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.